Krill were measured for total length (from behind the eye to the end of the telson) at 6X using a calibrated eyepiece reticle then flash frozen individually in liquid nitrogen. Total length was converted to dry weight (DW) using a published length-weight regression (Feinberg et al. 2007).
Protein content was determined according to the bicinchoninic acid (BCA) method (Smith et al. 1985) using a Pierce BCA Protein Assay Kit (Thermo Scientific).
ETS activity was assayed using the method of Owens and King (1975), as modified by Gómez et al. (1996), and adapted for a 96-well plate. Assays and blanks were measured in triplicate at 25 °C, calculated according to Packard and Christensen (2004), and corrected to in situ temperatures (depth integrated) using the Arrhenius equation with an activation energy of 15 kcal mol-1 (Packard et al. 1975) and standardized to protein specific activity, spETS.
AARS was measured following the method of Yebra and Hernadez-León (2004), modified by Yebra et al. (2011), and adapted for a 96-well plate (Yebra et al. 2017). All activities were corrected to in situ temperatures with the Arrhenius equation using an activation energy of 8.57 kcal mol-1 (Yebra et al. 2005) and standardized to protein specific activity, spAARS. spAARS_1 was measured with the NADH Blank and calculated as described by Mclaskey et al. (2020). For each sample, assays and NADH Blanks were measured in triplicate.
Oxygen consumption of individual krill was measured at 12 °C by closed-cell respirometry in 22-mL vials containing optical oxygen sensors (PSt7 PreSens) and a 12-mm magnetic stir bar separated from the animal by 200-μm mesh. Measurements were taken every 15 minutes for 2 hours. Krill were kept in filtered seawater to clear their guts for ~1 hr prior to respirometry.
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